Fiber optic transmission systems typically utilize an optoelectronic source such as a LED or a vertical cavity surface emitting laser (VCSEL) to generate optical signals for communication purposes. The optical signals are transmitted along optical glass fibers to a receiver diode or similar communications device where the optical signals are converted to electrical signals. For competitive reasons, optical networks support an ever increasing menu of products which require high bandwidth and very high fiber count cables. Such systems require an efficient and economical method for diagnosing problems among the individual optical lines and the optoelectronic devices.
A number of factors impact the efficiency of an optical communication system including the quality of the optical signal produced by the optoelectronic device and the construction and alignment of the optical path. The optical device ports must be aligned with the optical fibers and optical fibers must be properly aligned with connectors and transceiver packages. The alignment issue is exacerbated by the tendency to package the optoelectronic devices into an array which transmits multiple signal lines simultaneously. Consequently, each optoelectronic device is operatively connected to an optical path, all of which are disposed within cables and connectors designed to use the minimum amount of space.
An important element in the optical path is the mechanically transferable (“MT”) connector that is molded from composite plastics and has a standard dimension that can accommodate a plurality of optical fibers typically arranged in a linear array. Alignment of the connector is provided by a pair of precisely sized metal guide pins that fit into accurately molded guide pinholes in the connector parts. Typically, v-shaped fiber guiding grooves are molded into the connector body for aligning each fiber with the fiber holes at the interface. For higher fiber counts, 2-D array MT connectors have been developed which allow for up to 60 fiber pairs without changing the dimensions of the typical MT connector ferrule. The grooves are aligned by layer and the layers are then stacked to achieve higher fiber count connectors.
Fiber optic connectors can fail due to manufacturing errors, environmental fractures and improper handling. Manufacturing errors include broken fibers inside the ferrule or damage to the fiber buffer. Fibers may break due to poor construction of the fiber itself. Air voids in the epoxy that holds the fiber in place may cause the fiber to break free. Thermal expansion of the epoxy may also break the fiber. Other manufacturing problems result from poor ferrule end face quality. If the end face is under or over polished, it may not mate properly with the fiber optic connector. Furthermore, the connector body itself is constructed of many different parts. If these parts are not aligned properly there may be poor signal quality due to the connections. Typically such damage is not discovered until the fiber is in place.
Failures can also occur due to dropouts created by extreme vibration or shock loads. When the ferrule end face is damaged by vibrations, the glass fiber may be scratched or damaged leading to high insertion and return losses. Fiber optic connectors can also fail due to improper cleaning during the assembly process or simply by mating together two connectors that are incompatible. In addition to failures of connections and cable length, the lasing or detecting device may be the cause of system failure. These devices are subject to failure due to environmental stress and wear-out.
There is a need to be able to determine whether an individual fiber optic connection or fiber optic strand is providing the required signal quality. Likewise, it would be advantageous to selectively monitor the performance of an optoelectronic device without disconnecting the array from the optical pathway. Such a system would eliminate the costly down time and testing costs required to diagnose each individual fiber and devices off-line. Furthermore, an in-line diagnostic tool would eliminate the danger of further damaging a system during the test procedure.